The second half of the circuit is an inverting
integrator. The first op-amp
starts with its two inputs in an unknown state; let's say it starts
with + slightly higher than – (which is at ground). The op-amp greatly amplifies
this difference, bringing its output to the op-amp's
positive power supply voltage, its maximum output (15 V in this
case). With this positive input, the integrator's output falls at a
constant rate.

The 10k and 4k resistors act as a voltage divider which put the
first op-amp's + input 4/14ths of the way from the second op-amp's output to the first
op-amp's output. When this input reaches ground, then the first op-amp's
output switches polarity, and the integrator switches direction,
forming the other half of the triangle. When the first op-amp
switches polarity again, a new cycle begins.